Field of the Invention
This invention relates to a direction switchable ratchet device for a door operator which is capable of preventing a hand-operated mechanism of the door operator from being incorrectly mounted.
Brief Description of Prior Art
A general door operator that is provided to upward or downward move a movable barrier is powered by electricity. In the case of power failure, power interruption due to fire or malfunction of the door operator, shutting or opening the door may be difficult. In order to ensure that the door can be shut or opened in the case of power failure, power interruption or malfunction of the door operator, the door operator is normally provided with a hand-operated mechanism. For example, a transmission mechanism is provided to upward or downward move the movable barrier manually by pulling a pull chain.
Such a door operator further comprises an electromagnetic brake for holding the movable barrier at a desired position or a stationary position. Conventionally, the electromagnetic brake may be so configured that a brake disk normally biased by a spring is retracted away from a brake lining by an electromagnet so as to release a rotary shaft of the door operator in the course of upward or downward moving the movable barrier by electrically energizing an electric motor of the door operator and that the brake disk is biased by the spring and abutted against the brake lining so as to brake the rotary shaft of the door operator in the course of electrically de-energizing the electric motor and the electromagnet of the door operator.
U.S. Pat. No. 6,055,885 issued to the inventor discloses a pull chain disk of a hand-operated mechanism. The pull chain disk also serves as a brake mechanism. In the course of upward or downward moving the movable barrier by electrically energizing the electric motor of the door operator, the pull chain disk is retracted by the electromagnet so as to release the drive shaft. When the electric motor is electrically de-energized, the pull chain disk is biased by the spring and abutted against a brake disk, and a chain of the pull chain disk is pressed on the housing of the door operator by a pressing plate so that the rotary shaft of the door operator is braked. In the case of power failure, the movable barrier may be moved by simply pulling the chain without additional operation on the brake mechanism.
U.S. Pat. No. 6,092,582 discloses that in a manual mode, the rotary shaft of the door operator can be rotated manually by actuating a brake release lever and pulling a chain simultaneously after a safety lever is switched to an unlocked position.
A pull chain disk mechanism for manual operation will be used only in the case of power failure or power interruption, and thus it is rarely used and sometimes is only reserved for a critical situation. It may be inconvenient to hide the suspending chain of the pull chain disk mechanism. As a result, the door operator may have an unpleasant outlook and may be touched by a child intentionally or unintentionally. It is thus desirable to provide a mechanism for manually moving the movable barrier in the case of power failure or failure of the door operator, which is easy to operate, simple in structure, and cost-effective.